Measuring hydrogen (H2) is something we do
a lot of here at Nova. We can measure it in a mixed background of other gases,
or in a binary mixture of H2 in one other gas such as O2, N2, Ar, etc.
One application that generally requires H2
analysis in a binary mixture with N2 is fuel cell operation and development. We
were sent some pics a while back from a fuel cell manufacturer. They use Nova
instruments to measure H2.
From Wikipedia, a general description of
fuel cell operation is as follows:
Fuel cells come in many varieties; however, they all work in the same general manner. They are made up of three adjacent segments: the anode, the electrolyte, and the cathode. Two chemical reactions occur at the interfaces of the three different segments. The net result of the two reactions is that fuel is consumed, water or carbon dioxide is created, and an electric current is created, which can be used to power electrical devices, normally referred to as the load.
At the anode a catalyst oxidizes the fuel, usually hydrogen, turning the fuel into a positively charged ion and a negatively charged electron. The electrolyte is a substance specifically designed so ions can pass through it, but the electrons cannot. The freed electrons travel through a wire creating the electric current. The ions travel through the electrolyte to the cathode. Once reaching the cathode, the ions are reunited with the electrons and the two react with a third chemical, usually oxygen, to create water or carbon dioxide.
The most important design features in a fuel cell are:
- The electrolyte substance. The electrolyte substance usually defines the type of fuel cell.
- The fuel that is used. The most common fuel is hydrogen.
- The anode catalyst breaks down the fuel into electrons and ions. The anode catalyst is usually made up of very fine platinum powder.
- The cathode catalyst turns the ions into the waste chemicals like water or carbon dioxide. The cathode catalyst is often made up of nickel but it can also be a nanomaterial-based catalyst.
In the specific project from which the
field pictures were taken, the requirement was for measurement of 0-100.0 % H2.
The sample is typically 70-90% H2 in balance N2, and is obtained at the anode
portion of the fuel cell. Measuring the H2 here is useful in evaluating what the
cell’s power output will be.
The sample itself is clean and basically
dry, with the possibility of occasional moisture in some operation conditions.
The gas analyzer has a condensate collection system and a liquid block membrane
to avoid water infiltration to the detector. The sample gas is under pressure
up to 1.2 barg (17psig). The analyzer has a built-in regulator. The fuel cell
manufacturer uses a peristaltic pump to push the sample that is vented out of
the analyzer back into the process to maintain the system gas composition.
Connection to the analyzer itself is quite
simple, as shown in this picture.
One potential safety concern is related to
the possibility of a gas leak occurring inside the analyzer cabinet. We can
offer an ex-proof leak detector that is mounted in the cabinet which will
de-power the analyzer in the event of a leak. To actively dilute a potential
leak, we can also arrange a continuous vent flow through the analyzer using a
fan. This is only suitable in clean environments with stable warm temperatures.
On this project, the fuel cell manufacturer
and end-user have been very happy with the Nova units. They have since ordered
a few spare filters in anticipation of normal maintenance.
For information on these and other gas
analyzer systems, give Mike or Dave at Nova a call, or send us an e-mail.
If you have any Nova instruments at your
plant or lab and want to share a couple of photos, feel free to send them to us
along with a brief explanation of your application.
1-800-295-3771
sales at nova-gas dot com
websales at nova-gas dot com
http://www.nova-gas.com/
*Fuel cell diagrams from Wikipedia, in public domain.
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